Monday, March 24, 2008

Banded Orb-weaving Spider, Argiope trifasciata

A fast moving spider in a football jumper

The Banded Orb-weaving Spider, also known as a Banded Garden Spider, has a bright banded yellow, white and black abdomen, but instead of standing out like a sore thumb, in its habitat it blends in remarkably well. This spider constructs a modest sized vertical web (about knee high) amongst sedge or grass, which provides an environment of green, yellow and black streaks, the perfect background to her camouflage. Here the large female remains motionless, head down day and night, remaining safe and overlooked by most predators.

The Banded Orb-weaving Spider, Argiope trifasciata

The underside is just as colourful

When under threat the female banded spider will suddenly drop to the ground and seek shelter in the tangled vegetation. But should an insect fly into her web, she rockets from her resting-place, and has the intruder silk wrapped within a blink of an eye. It is then bitten on or near the head, after which she will return to the centre of the web until her venom has paralysed the intruder. She will then return and wrap her meal even more securely.

The first paralysing bite into a March Fly

The female Banded Spider is around 2 cm in length (excluding legs), so a reasonably large orb-weaving species. It is a little larger than the closely related St. Andrews Cross Spider, Argiope aetherea. This spider is well known for the bright white cross made from non-capture silk in the centre of the web, called the stabilimenta. The spider rests on this formation also in the shape of a diagonal cross, with its legs outstretched and arranged in pairs.

The Banded Spider also rests in the shape of a diagonal cross, but seldom weaves a stabilimenta, or if so, only a partial one. A study published in the scientific magazine Behavioral Ecology suggests that the bright-white stabilimenta is made to make the web more visible to flying birds and so reduce web damage from accidental collisions. It is a trade-off however, as the web also becomes more visible to flying insects and so the spider's catch is reduced.

In the Esperance region, the Banded Spider seldom weaves a stabilimenta, possibly because they construct their nests close to the ground where local birds seldom fly. Whereas the St. Andrews Cross Spider when mature (an Eastern States species not found in WA), always construct a stabilimenta, but they generally build their webs at a higher elevation and more likely in the flight-path of birds.

A partial white stabilimenta at bottom right of center

Banded Orb-weaving Spider, Argiope trifasciata

In Australia the Banded Spider is only recorded in Queensland and WA, but is found in many other parts of the world with a major exception of Europe. They do vary slightly in size, but coloration and behaviour are similar, so is the low-lying habitat amongst grass and sedges, so the international banded spider is not currently considered evolved sufficiently (due to their wide separation) into different species.

A popular habitat is a low-lying sedge area, surrounded by grasstrees

The male banded spider is a fraction the size of the female (usually between a third and a quarter) and sometimes with other males, can be found on the outer edge of the web. It is very hazardous however being a suitor to the large female, as many males end up being her lunch; those that do escape often have to shed a leg or two to distract her in the process.

A fully intact male Banded Spider

A male Banded Spider who has lost the back legs escaping the female

For reasons possibly related to nursery duties, the female will leave her web unattended. On one such occasion a very bold male took her place in the centre of the web, but alas his triumph was short lived, as next day he looked like a silk-wrapped snack.

The female Banded Spider snacking on the unfortunate male

Despite having very effective venom for paralysing invertebrates, banded spiders are harmless to humans preferring to flee and play dead rather than bite. And unless you are looking in the right place, you will probably never see one, but should you be so lucky, it is worth checking this spiders activities daily, for besides being very colorful, they are also interesting to know.

The underside of the female Banded Spider, note the broad spinneret region for fast wrapping

9 comments:

MissAnthropy
said...

The male banded spider is a fraction the size of the female (usually between a third and a quarter) and sometimes with other males, can be found on the outer edge of the web. It is very hazardous however being a suitor to the large female, as many males end up being her lunch; those that do escape often have to shed a leg or two to distract her in the process.

Size *does* matter, at least in this case ;)

Stunning photos, as always, and the story (also 'as always'), so deceptively easy to read, that one hardly realises how much one is learning.

I found one of these in my front garden this evening, in a web at the top of a blackboy. My wife wanted to kill it but I said no it is probably not dangerous and we left it there. Now I know how lucky we are to have it there I will check it tomorrow. I took some good photos if anyone is interested. My email is node09@gmail.com

My Other Blogs

There are three blogs that I manage, so if you find one with no recent posts, please try one of the others. They all deal exclusively with the flora and fauna of the Esperance region of Western Australia, so may also be of interest.

About Me

An ardent nature lover who is happiest when in the bush. The object of this blog is to record the nature around me, particularly the unusual or rarely encountered flora and fauna. My photography is governed by my equipment that being a modest Canon A80 PowerShot Camera with standard lens. So I do not set out to portray subjects in high photographic detail, but to show them in an interesting pose and to highlight species characteristics.